This invention relates to a method of preparing a foundation structure, a foundation structure prepared by such a method and an apparatus used for preparing such a foundation structure.
U.S. Pat. No. 5,181,797 discloses a method and apparatus for in-situ solidifying and stabilising a mass of unstable foundation soil. A plasma arc torch is inserted into a drilled and cased hole to a selected depth in a subterranean unstable soil layer. The torch is then energised and the heat generated by the torch melts the soil material close to the hole, to form a pool of melt while more remote sections are baked to a brick-like consistency or dried and strengthened. Upon cooling, the central melted soil material cools to a hard, vitrified column with physical properties equivalent to hard dense rock.
A first disadvantage of this method of solidifying and stabilising unstable foundation soil is that it requires an excessive amount of energy to heat the soil to a relatively high temperature (4000° C. to 7000° C.) to form the plurality of columns from melted soil, making the method not economically viable.
A second disadvantage of the above method of stabilising unstable foundation soil is that it takes a relatively long time to prepare the holes in the soil before the torch is inserted into the hole and energised. After the holes are dug, they are first lined with a tubular heat destructible casing. This makes the method even more uneconomical.